1. Field of the Invention
The present invention relates to an optical filter for plasma displays, and more particularly, to an optical filter for a plasma display with superior transmittance and reflectivity characteristics.
2. Description of the Related Art
Plasma displays, which generate the visual image by discharging a gas plasma, have been attractive as a substitute for cathode ray tubes (CRTs) due to good display performance thereof, in terms of display capacity, luminance, contrast, reflection image and viewing angle. In plasma displays, application of a direct or current voltage between electrodes creates a discharge of gas plasma therein, resulting in the emission of ultraviolet (UV) light from the gas plasma. The UV emission, in turn, excites adjacent phosphor materials resulting in electromagnetic emission of visual light.
FIG. 1 is an exploded perspective view of the configuration of a common plasma display, and FIG. 2 is an exploded perspective view of a part of the panel assembly in FIG. 1.
Referring to FIG. 1, the plasma display device includes a case 11, a cover 15 of the case 11, and a driving circuit board 12, a panel assembly 13 and an optical filter 14, which are accommodated in the case 11. The panel assembly 13 has a configuration shown in FIG. 2. Referring to FIG. 2, a series of first electrodes 23a as transparent display electrodes, a series of second electrodes 23b as address electrodes, are arranged between a front glass substrate 21, and a rear glass substrate 22. The first electrodes 23a and the second electrodes 23b are formed on the opposed inner surfaces of the front glass substrate 21 and the rear glass substrate 22, respectively, perpendicular to each other. A dielectric layer 24xe2x80x2 is formed over the second electrodes 23b on the rear glass substrate 22 and a series of barrier walls 27 are formed on the dielectric layer 24xe2x80x2 to define cells 29 therebetween. The cells 29 are filled with an inert gas such as argon (Ar). Also, a phosphor 28 is deposited on a predetermined region between the barrier walls 27, i.e., on a predetermined region of the cells 29. A dielectric layer 24 is formed over the first electrodes 23a and a protective layer 25 is formed thereon.
The driving circuit board 12 of FIG. 1 includes a variety of electronic parts for applying a voltage to the panel assembly 12 to drive the first and second electrodes 23a and 23b formed therein, thereby electrically controlling the overall display operation. The optical filter 14 disposed in front of the panel assembly 13 protects the viewer from electromagnetic waves generated by the panel assembly 13 and prevents a reflection of ambient light. FIG. 3 shows the intersection of the optical filter 14.
Referring to FIG. 3, the known optical filter in the art includes a transparent substrate 31, an antireflective layer 32 on the front surface of the transparent substrate 31, for preventing ambient light reflections, and an electromagnetic wave shield 30 on the rear surface thereof.
The antireflective layer 32 is formed of a material, for example, silicon oxide or titanium dioxide, and the electromagnetic wave shield 30 is formed of a material having superior conductivity, for example, silver (Ag). The electromagnetic wave shield 30 is grounded through the cover 15 and to the case 11. In other words, the electromagnetic waves from the panel assembly 13 are shielded by the electromagnetic shield 30 and grounded through the cover 15 and to the case 11 before they reach the viewer. For this purpose, the electromagnetic wave shield 30 of the optical filter 14 is electrically connected to the cover 15 and the case 11.
However, the conventional optical filter has the following-disadvantages. Since the reflectivity of the silver layer used as an electromagnetic wave shield is slightly high as a level of 10%, an antireflective layer is further required. In addition, since the optical filter cannot almost shield infrared (IR) light radiated from the panel assembly, an IR shield (not shown) must be interposed between the electromagnetic wave shield and the panel assembly, which avoids a misoperation of the display adopting the optical filter. Also, the optical filter reduces visible light transmittance and in turn contrast characteristic. Poor luminance characteristic of blue phosphor, relative to that of red and green phosphors, increases a need for color correction in the blue visible wavelength range.
It is an objective of the present invention is to provide an optical filter for plasma displays with antireflective properties and effective electromagnetic wave and infrared (IR) light shielding effects, in which a decrease in reflectivity in the visible wavelength range enhances a contrast characteristic and assures color correction in the blue visible wavelength range.
To achieve the above objective, the present invention provides an optical filter for a plasma display comprising: a transparent substrate; a first transparent dielectric layer formed on the transparent substrate with at least one metal oxide selected from the group consisting of titanium dioxide (TiO2), zinc oxide (ZnO), indium oxide (In2O3), tin oxide (SnO2) and cadmium oxide (CdO), or materials obtained by doping the metal oxides with at least one metal selected from the group consisting of indium (In), gallium (Ga), aluminum (Al), tin (Sn) and antimony (Sb); a silver (Ag) layer formed on the first transparent dielectric layer; a metal silver-diffusion barrier layer formed on the silver layer, for suppressing diffusion of silver into the overlaying layer; and a second transparent dielectric layer formed on the metal silver-diffusion barrier layer with at least one metal oxide selected from the group consisting of titanium dioxide (TiO2), zinc oxide (ZnO), indium oxide (In2O3), tin oxide (SnO2) and cadmium oxide (CdO), or materials obtained by doping the metal oxides with at least one metal selected from the group consisting of indium (In), gallium (Ga), aluminum (Al), tin (Sn) and antimony (Sb).